In recent years, the appearance of small, multifunctional electronic parts of a device permitted the device to become smaller and have more functions.
Interconnects to apply electrical signal is to the electric parts became ultra-small correspondingly.
However, this reduction in size also caused a side effect on interconnects, such as open circuits, and increased the incidence of failure in the device.
Various devices and methods have been suggested to test defects on interconnects in devices, which occurs after the device has been manufactured.
Conventionally, optical microscopes have been commonly used to examine defects in a pattern. However, the optical microscope has a problem it may confuse defects in a pattern with contaminants residing on the surface of a DUT. Moreover, the DUT needs to be dismantled to detect inner defects.
Also, it takes fairly much time to perform a test since each of multiple circuit patterns should be examined by an operator, and the results of the test may change depending on the operator's skills.
U.S. Pat. No. 5,106,213 discloses a device for testing a flat display device using polymer dispersed liquid crystal (PDLC), which includes a reflecting film (not shown in drawings), a lower indium tin oxide (ITO) electrode (not shown in drawing), a PDLC electrode layer (not shown in drawings), and an upper ITO electrode (not shown in drawings) stacked in this order.
PDLC molecules are randomly arranged when no voltage is applied between the upper ITO electrode and the down ITO electrode. Accordingly, the incident light from the upper ITO electrode is dispersed at the upper ITO electrode.
When a voltage is applied between the upper ITO electrode and the lower ITO electrode, the PDLC molecules are uniformly arranged, and therefore, the incident light from the upper ITO electrode passes through the upper ITO electrode, the PDLC layer, and the lower ITO electrode in the order thereof, and then reflects by the reflecting layer.
It can be determined whether or not there are defects on each circuit corresponding to each pixel of a flat display device by the above operation principle.
The testing device is placed on the surface of a flat display device (not shown) on which a plurality of pixels are arranged in a matrix, as being spaced from the surface of the flat display device by a constant distance. A high level voltage is applied between the flat display device and the testing device.
No electric field is generated at the PDLC layer around a bad pixel region since a TFT corresponding to the bad pixel region does not have a good electrical property around the bad pixel region. As a result, the molecules in the PDLC layer a round the bad pixel region are not arranged in a uniform manner, and this leads to deterioration in reflectivity of the testing device around the bad pixel region.
On the contrary, a TFT corresponding to a normal pixel region has a good electrical property around the normal pixel region, and therefore, electric fields may be easily generated at the PDLC layer around the normal pixel region. Accordingly, the PDLC molecules are uniformly arranged around the normal pixel region and the reflectivity of the testing device increases around the normal pixel region.
A pre-installed charge-coupled device (CCD) camera generates an electrical signal corresponding to the intensity of light reflected by the testing device.
A pre-installed image processor converts the electrical signal transmitted from the CCD camera into an image.
However, it is necessary to keep the testing device spaced from the DUT, i.e. the flat display device, by several micrometers to make the PDLC molecules react with electric fields. Accordingly, the testing device could be damaged by minute particles residing on the flat display device.
In terms of a property of the PDLC, its lowered sensitivity causes a necessity of applying a high-level voltage between the flat display device and the testing device to compensate for it. And, the distance between the testing device and the flat display device needs to be small since a weak electric field is produced in spite of the application of a high-level voltage between the flat display device and the testing device. As a consequence, the testing device is damaged by minute particles residing on the flat display device because the distance between the testing device and the flat display device is narrow as described above.